The present invention relates to a manufacturing method of right and left spectacle lenses and system thereof. Particularly, the present invention is effective when the right and left spectacle lenses have different focal powers to each other. The spectacle lenses may be single-vision lenses or progressive-power lenses.
Spectacles consist of right and left lenses and a frame that holds these lenses. When the powers required for the right and left lenses are equal to each other, shapes of the front surface (an object side) and the back surface (an eye side) of the right lens are the same as that of the left lens. On the other hand, when right and left lenses whose powers required are largely different are independently designed, the shape of the right lens is largely different from the shape of the left lens, which loses a balance between the shapes of the right and left lenses, exacerbating an outward appearance thereof. Since the outward appearance depends on the shapes of the front surfaces, the shapes of the front surfaces should be identical with each other to enhance the outward appearance.
A technique to equate shapes of front surfaces to keep the balance between right and left lenses has been known as prior art. For instance, Japanese patent provisional publication No. Hei 8-320457 discloses the technique to independently design shapes of right and left lenses according to a prescription at a first step, and to redesign at least one of the right and left lenses so that the curvatures of the front surfaces are approximate to each other.
However, the above described publication does not describe optical performances of right and left lenses after the redesigning. In general, since a lens form (i.e., a combination of shapes of front and back surfaces) to produce the given focal power is limited to minimize aberrations, when the lens is redesigned with only considering the shapes of the front surfaces, the aberrations becomes large, exacerbating the optical performance.
Namely, in the case of a spherical lens, a lens form to minimize aberrations is substantially uniquely determined with respect to the focal power when the lens material is predetermined. Therefore, when the focal powers required for right and left lenses are different to each other, the aberrations of at least one of the right and left lenses must increase as a result of redesigning to equate the shapes of the front surfaces.
On the other hand, in the case of an aspherical lens, a range of choices of shapes for a specific refractive power is broader than in a spherical lens. However, when the difference between the focal powers of the right and left lenses becomes large, it is inevitable that the aberration increases due to the redesigning. A conventional aspherical spectacle lens has an aspherical front surface and a spherical back surface. Semifinished lens blanks whose aspherical front surfaces are finished are stockpiled in a manufacturing factory. In a conventional manufacturing method, shapes of front surfaces of right and left lenses are determined among various predetermined shapes based on specifications of a customer in a first step. In a second step, curvatures of back surfaces of the right and left lenses are calculated on the basis of the specification and the determined shape of the front surfaces. In an actual processing step, a pair of semifinished lens blanks are selected among various stockpiled blanks and they are placed on a surface processing machine. Then, the back surfaces of the selected semifinished lens blanks are processed with the surface processing machine on the basis of the calculated curvatures. There are different types of semifinished lens blanks corresponding to various focal powers. That is, the entire range of a focal power required for a spectacle lens is divided into a plurality of sections and each aspherical surface is assigned to each section. Since processing of an aspherical surface was difficult with the conventional processing machine, it was important to limit the types of aspherical surfaces in order to reduce manufacturing cost.
Each aspherical surface is designed so as to keep an optical performance when the aspherical surface covers the focal power within the specific section. Therefore, when a lens having a predetermined focal power is manufactured using an aspherical surface that is assigned to a different section, the optical performance becomes worse significantly. Namely, when the aspherical front surfaces of right and left lenses whose focal powers are not within the same section are formed to be identical, an optical performance of either right lens or left lens that employs an aspherical surface of the different section becomes worse significantly.
Design examples of conventional single-vision spherical lenses and conventional single-vision aspherical lenses will be described.
FIGS. 39A and 39B are sectional views of the conventional spherical lenses when the right and left lenses are independently designed. In the drawings described below, (R) represents the right lens and (L) represents the left lens. In each lens diagram, the surface at the left is a front surface and the surface at the right is a back surface. In this example, spherical powers (SPH) required for the right and left lenses are xe2x88x924.00 diopter and +2.00 diopter, respectively. TABLE 1 shows numerical construction of each lens. In TABLE 1, R1 denotes a radius of curvature of the front surface, R2 denotes a radius of curvature of the back surface, T denotes a center thickness, N denotes a refractive index and xcfx86 denotes a diameter of the semifinished lens blank. Units of R1, R2, T and xcfx86 are millimeters (mm).
Base curves (surface power of front surface) of the right and left lenses are 4.00 diopter and 7.00 diopter, respectively. FIGS. 40A and 40B show astigmatisms of the right and left lenses. In each of graphs, a solid line represents the astigmatism A∞ for distance vision (object distance: ∞) and a dotted line represents the astigmatism AS300 for near vision (object distance: 300 mm). In the graphs of astigmatism, the horizontal axis denotes an amount of astigmatism (unit: diopter) and the vertical axis denotes a visual angle (unit: degree).
The respective spectacle lenses have satisfactory optical performances, while the outward appearance lacks in balance between the right and left lenses because of the difference between the base curves. Thus, the design of the left lens will be changed such that the base curve of the left lens matches to that of the right lens. Numerical constructions after the design change are shown in TABLE 2. FIGS. 41A and 41B show sectional views of the spectacle lenses after the design change. FIGS. 42A and 42B show astigmatisms AS∞ for distance vision and the astigmatism AS300 for near vision of the spectacle lenses after the design change.
Since the base curves of the right and left lenses become identical (4.00 diopter), the front surfaces have the common shape. As shown in FIG. 42B, however, the astigmatism of the left lens for distance vision becomes significantly large as compared with the condition before the design change.
Next an example of aspherical lenses will be described. FIGS. 43A and 43B are sectional views of the conventional aspherical lenses that are independently designed. The front surfaces are rotationally symmetrical aspherical surfaces and the back surfaces are spherical surfaces. In this example, SPH required for the right and left lenses are xe2x88x924.00 diopter and xe2x88x928.00 diopter, respectively. TABLE 3 shows numerical construction of each lens. R1 represents a radius of curvature at the center.
FIGS. 44A and 44B are graphs showing variations of surface powers of the front surfaces. The variation of the surface power is represented as a difference between the surface power at a point along a meridional plane and the paraxial surface power. In the graphs of surface power, the horizontal axis denotes the difference of the surface powers and the vertical axis denotes the distance from the center of the front surface (unit: mm). The base curves of the right and left lenses are 2.00 diopter and 0.50 diopter, respectively. FIGS. 45A and 45B show astigmatisms AS∞ for distance vision and the astigmatism AS300 for near vision.
The respective spectacle lenses have satisfactory optical performances, while the outward appearance lacks in balance between the right and left lenses because of the difference between the base curves. Thus, the design of the left lens will be changed such that the base curve of the left lens matches to that of the right lens. Numerical constructions after the design change are shown in TABLE 4. FIGS. 46A and 46B show sectional views of the spectacle lenses after the design change. FIGS. 47A and 47B show variations of surface powers of the spectacle lenses after the design change. FIGS. 48A and 48B show astigmatisms AS∞ for distance vision and the astigmatism AS300 for near vision of the spectacle lenses after the design change.
Since the base curves of the right and left lenses become identical (2.00 diopter), the front surfaces have the common shape. As shown in FIG. 48B, however, the astigmatism of the left lens for near vision becomes significantly large as compared with the condition before the design change.
The above described problem also holds true for progressive-power spectacle lenses.
When a progressive-power lens designed by a spherical design method, a lens form to minimize aberrations is substantially uniquely determined with respect to the focal power when the lens material is predetermined. Therefore, when the focal powers required for right and left progressive-power lenses are different to each other, the aberrations of at least one of the right and left progressive-power lenses must increase as a result of redesigning to equate the shapes of the front surfaces.
The spherical design method is the method in which a main meridian that extends across the progressive-power surface in an up-and-down direction is designed as an umbilical line having no surface astigmatism.
On the other hand, an aspherical design method is the method in which the main meridian is designed as a non-umbilical line having surface astigmatism. Since the aspherical design method has a higher degree of flexibility than the spherical design method, the progressive-power surface designed by the aspherical design method can keep a satisfactory optical performance while using a smaller curvature surface than the surface designed by the spherical design method.
According to the aspherical design method, the range of shapes to select from becomes wider than the case when the surface is designed by the spherical design method. However, when the difference between the focal powers required for right and left progressive-power lenses becomes large, increasing of the aberrations due to the redesigning is inevitable.
A conventional progressive-power spectacle lens has a progressive-power surface as a front surface and a spherical surface or a toric surface as a back surface. Progressive-power semifinished lens blanks whose progressive-power front surfaces are finished are stockpiled in a manufacturing factory. A back surface of a progressive-power semifinished lens blank is processed to adjust the curvature thereof based on specifications of a customer. There are different types of progressive-power semifinished lens blanks corresponding to various focal powers. Each progressive-power surface is assigned to each section. Since processing of a progressive-power surface was difficult with the conventional processing machine, it was important to limit the types of progressive-power surfaces in order to reduce manufacturing cost.
Each progressive-power surface is designed so as to keep an optical performance when the progressive-power surface covers the focal power within the specific section. Therefore, when a lens having a predetermined focal power is manufactured using a progressive-power surface that is assigned to a different section, the optical performance becomes worse significantly. Namely, when the progressive-power front surfaces of right and left lenses whose focal powers are not within the same section are formed to be identical, an optical performance of either right lens or left lens that employs a progressive-power surface of the different section becomes worse significantly.
Design examples of conventional progressive-power lenses designed by the spherical design method and conventional progressive-power lenses designed by the aspherical design method will be described.
FIGS. 49A and 49B are sectional views of the conventional progressive-power lenses that are independently designed by the spherical design method. The front surfaces are progressive-power surface and the back surfaces are spherical surfaces. In this example, spherical powers (SPH) at a distance portion required for the right and left lenses are xe2x88x924.00 diopter and +2.00 diopter, respectively. An addition power (ADD) is 2.00 diopter for both of the right and left lenses. TABLE 5 shows numerical construction of each lens. In TABLE 5, D1 denotes a surface power of the front surface at the distance portion, D2 denotes a surface power of the back surface. Units of D1 and D2 are diopter. The mark xe2x80x9c*xe2x80x9d attached to D1 or D2 represents that the marked surface is a progressive-power surface.
FIGS. 50A and 50B are graphs showing variations of surface powers of the progressive-power front surfaces of the right and left lenses. In the graphs, a solid line represents the surface power DM in a vertical direction along the main meridian and a dotted line represents the surface power DS in a horizontal direction. Base curves (surface power in the distance portion of front surface) of the right and left lenses are 4.00 diopter and 7.00 diopter, respectively. There are no surface astigmatisms (i.e. difference between DM and DS), because the lenses are designed by the spherical design method.
FIGS. 51A and 51B are graphs showing variations of xe2x80x9cas-wornxe2x80x9d powers of the right and left lenses. The horizontal axis denotes the xe2x80x9cas-wornxe2x80x9d power (unit: diopter) and the vertical axis denotes the distance from the center of the front surface (unit: mm). In the graphs, a solid line represents the xe2x80x9cas-wornxe2x80x9d power PM in a vertical direction along the main meridian and a dotted line represents the xe2x80x9cas-wornxe2x80x9d power PS in a horizontal direction.
The respective spectacle lenses have satisfactory optical performances, while the outward appearance lacks in balance between the right and left lenses because of the difference between the base curves. Thus, the design of the left progressive-power lens will be changed such that the base curve of the left progressive-power lens matches to that of the right lens. Numerical constructions after the design change are shown in TABLE 6. FIGS. 52A and 52B show sectional views of the progressive-power spectacle lenses after the design change.
FIGS. 53A and 53B are graphs showing variations of the surface powers DM and DS after the design change. FIGS. 54A and 54B are graphs showing variations of the xe2x80x9cas-wornxe2x80x9d powers PM and PS after the design change. The base curves of the right and left progressive-power lenses become identical (4.00 diopter) and the front surfaces have the common shape. As shown in FIG. 54B, however, the astigmatism (i.e., difference between PM and PS) of the left lens becomes significantly large as compared with the condition before the design change.
FIGS. 55A and 55B are sectional views of conventional progressive-power lenses designed by the aspherical design method that are independently designed. The front surfaces are progressive-power surface and the back surfaces are spherical surfaces. In this example, SPH at a distance portion required for the right and left lenses are xe2x88x924.00 diopter and xe2x88x928.00 diopter, respectively. ADD is 2.00 diopter for both of the right and left lenses. TABLE 7 shows numerical construction of each lens.
FIGS. 56A and 56B are graphs showing variations of the surface powers DM and DS. Base curves of the right and left lenses are 2.00 diopter and 0.50 diopter, respectively. FIGS. 57A and 57B are graphs showing variations of the xe2x80x9cas-wornxe2x80x9d powers PM and PS.
The respective spectacle lenses have satisfactory optical performances, while the outward appearance lacks in balance between the right and left lenses because of the difference between the base curves. Thus, the design of the left progressive-power lens will be changed such that the base curve of the left progressive-power lens matches to that of the right lens. Numerical constructions after the design change are shown in TABLE 8. FIGS. 58A and 58B show sectional views of the progressive-power spectacle lenses after the design change.
FIGS. 59A and 59B are graphs showing variations of the surface powers DM and DS. FIGS. 60A and 60B are graphs showing variations of the xe2x80x9cas-wornxe2x80x9d powers PM and PS. The base curves of the right and left progressive-power lenses become identical (2.00 diopter) and the front surfaces have the common shape. As shown in FIG. 60B, however, the astigmatism of the left lens becomes significantly large as compared with the condition before the design change.
The above examples of the conventional single-vision spectacle lenses and the conventional progressive-power spectacle lenses show that the outward appearance and the optical performance are mutually contradictory requirements under the conventional design method when the focal powers required for the right and left lenses are different to each other. That""s because the conventional design method only takes the focal powers and the shapes into account.
It is therefore an object of the present invention to provide improved manufacturing method and system of spectacle lenses, which is capable of manufacturing spectacle lenses that are balanced in an outward appearance and have satisfactory optical performance.
For the above object, according to the present invention, there is provided an improved manufacturing method of spectacle lenses, which includes:
selecting and determining a substantially common shape for front surfaces of right and left lenses among predetermined shapes based on specifications of the right and left lenses;
calculating shape data of back surfaces of the right and left lenses, respectively, on the basis of the specifications and the selected shape of the front surfaces;
processing a back surface of a semifinished lens blank whose front surface is finished with an aspherical surface processing machine controlled based on the shape data of one of the right and left lenses; and
processing a back surface of a semifinished lens blank whose front surface is finished with the aspherical surface processing machine based on the shape data of the other lens.
With this method, the manufactured spectacle lenses are balanced in the outward appearance because the front surfaces are substantially identical to each other. Further since the shapes of the back surfaces can be determined so as to reduce aberrations, the manufactured lenses having satisfactory optical performances can be obtained. The xe2x80x9csubstantially common shapexe2x80x9d means that the difference between the front surfaces of the right and left lenses is smaller than the difference between the independently designed lenses. It is desirable that the shapes of the front surfaces are in perfect agreement with each other. However, the outward appearance can be enhanced even if the shapes are slightly different.
The spectacle lenses may be single-vision lenses or progressive-power lenses. When the single-vision lenses are manufactured, the specifications preferably include spherical powers and cylindrical powers of the right and left lenses, respectively. When the progressive-power lenses are manufactured, the specifications preferably include vertex powers of distance portion and addition powers of the right and left lenses, respectively.
The selecting and determining the shape of the front surfaces and the calculating shape data of the back surfaces are preferably implemented via computer program. In such a case, the aspherical surface processing machine is operated under computer control based on the calculated shape data of the back surfaces. Further, the calculating the shape data of the back surfaces may be implemented via computer program with an optimization algorithm so as to reduce aberration while keeping a required focal power.
When the common shape of the front surface is a spherical surface, the processing of the front surface is easy. The common shape may be an intermediate shape between the shapes of the independently designed lenses or may be in agreement with one of the independently designed lenses.
A manufacturing system of spectacle lenses according to the invention includes:
an input device that is employed to input specifications of right and left lenses;
a selecting device for selecting and determining a substantially common shape for front surfaces of the right and left lenses among predetermined shapes based on the specifications;
a calculating device for calculating shape data of back surfaces of the right and left lenses, respectively, on the basis of the specifications and the selected shape of the front surfaces;
an aspherical surface processing machine that process a back surface of a semifinished lens blank; and
a controlling device for controlling the aspherical surface processing machine to process the semifinished lens blanks based on the shape data of back surfaces of the right and left lenses.
The selecting device, the calculating device and the controlling device are preferably implemented via computer program.